[clang] [clang-tools-extra] [lldb] [llvm] [Support][JSON] Use `std::unordered_map` for object storage (PR #171230)

[Zixu Wang via cfe-commits]

zixu-w wrote:

Also I'm wondering should I wrap the iterator in a wrapper that in some way exposes `getFirst()` and `getSecond()`, to help with the change and also prevent downstream failures. The JSON parser is a widely used utility and lots of things would break. Or maybe not worth it?

https://github.com/llvm/llvm-project/pull/171230